Photo-electric device



June 30, 1931. T RY, R 1,812,764

I PHOTO ELECTRIC DEVICE Original Filed April 6, 1925 rjLighfz sensikive slfrfiacevi. I

- lhventor Willi m IE.StorgJ'r-, by

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Patented June 30, v1931 UNITED s' xaras PATENT OFFICE WILLIAM E. STORY, JR., F WORCESTER, MASSACHUSETTS, ASSIGNOR T0 GENERAL ELECTRIO COMPANY, A. CORPORATION OF NEW YORK 4 PHOTO-ELECTRIC DEVICE Original application filed April 6, 1925, Serial No. 20,007. Divided and this application filed April 25,

1929. Serial li'o. 358,070.

My invention relates to hoto-electric cells, and more particularly to t e use of such cells as a means for comparing the intensity of light from two sources.

This application is a division of my prior application Serial No. 20,907, filed April 6, 1925 and entitled Photo-electric devices.-

It is an object of my invention to provide means whereby the intensity of light from two sources may be compared by means of a photo-electric device in each of the two arms of a Wheatstone bridge, and in particular to compare the illumination from any lamp with that from a standard lamp in such a rors at present avoided onl by the use of way as to avoid not only the visual comparison of illumination, but also some of the crcomplicated and often unsa'tlsfactory means.

When two photo-electric cells are employed to' compare the intensity of light from two sources, the accuracy of the comparison de pends upon a constant ratio of sensitivity of the two cells, and it is a further-object of. my invention to improve the constancy of this ratio.

With given terminal potential and given illumination the current from a photo-electric cell depends almost entirely upon two factors, first on the condition. of the sensitive surface, and second on the kind and pressure of the gas within the container. The gas pressure may change due to absorption by bombardment of the sensitive surface or by gas previously absorbed coming ofl again, or by a very slow leak, or by changes in temperature of different parts of the container. In order to cause such changes to affect both cells alike I have employed two cells in a single container. By the use of a double photoelectric cell the gas pressure and temperature will be alike on both sides of the cell and the ratio of the sensitivities of the two-halves of the cell will, therefore, remain relatively conbest be understood by reference to the fol:

nated as 1 a photo-electric cell of substantially spherical form and containing an inert gas such as argon. A thin light-excluding metal film 2 covers the interior of l the cell with the exception of two oppositely located windows 3 and 4; through which light may be admitted from a standard lamp 5 and a lamp 6, of the same type as a lamp to be tested. The cathode element 7 of the cell may comprise a substantially flat silver covered glass plate this formation being coated on opposite sides thereof with a light-sensitive substance such as potassium and is supported centrally of the cell by means of wires, not shown. As thus. disposed within the cell the light sensitive surfaces separate the cell into two compartmen'ts in such a way as to prevent an appreciable amount of either light or electrons in one compartment from reaching the other compartment, although space is allowed for equalization of gas pressure in the two compartments. The anodes 8 of the cell are looated on opposite sides of the cathode 7 and are connected through "resistances 9 and 10 to one of the leads of a direct current source of power. The other direct current lead is connected to the two light sensitive surfaces of the cathode 7. A galvanometer 11 and switch 12 are connected across the arms of the-Wheatstone bridge in the usual manner. Variable resistances 13 and 14 connect the lamps to be compared with a common source of current supply.

In the operation of the device high resistances 9 and 10 are included in two of the arms of the Wheatstone bridge. The reading on the galvanometer is then reduced to zero by re lating the distance'of lamp 6 from one o the cells, while maintaining the standard lamp 5 at amonvenient fixed distance from the other cell, the light of each lamp being the only light falling on the corresponding cell. After this adjustment is made for zero current through the galvanometer T the standard lamp 5 is replaced in turn by each of the'lamps to be tested and the galvanometer reading again adjusted to zero by moving the lamps to be tested. The distance from the cell at which each lamp will give the same illumination as the standard lamp at the distance at which it was placed in the first comparison is thus determined and the relative illumination of the lamps are easily calculated or read off on a suitably graduated scale. In this manner the operator is relieved of the dilficulty of judging light intensities, and any variation in the intensity of light from the two sources is indicated by the movement of the galvanometer needle.

By connecting the lamps to a common source the readings of the galvanometer are unaifected by small changes in line voltage. However, if the supply line is subject to wide fluctuations in voltage care should be taken to see that the conductivity of the cells is proportional to the light falling upon them for the potential and light range used. In general variations of line potential will cause the same changes in illumination of the two lamps if the lamps are of the same type and run at the same potential.

While the cathode sensitized on both sides divides the cell in such a way that neither light nor electrons in one compartment can get into the'other compartment, such an arrangement, although in general desirable, is not necessary since the effect on one circuit by the constant light from the other lamp can be kept constant and the adjusment made 1for a constant additional light from the first amp. 7

While I have shown a double photo-electric cell, two complete cells connected together by a tube would serve the same purpose ex cept for inaccuracies which might be caused by unequal changes of temperature. Various other modifications in the manner of carryingmy invention into effect will readily suggestthemselves to persons skilled in the art without departing from the scope of my invention as set forth in the appended claims.-

What I claim as new and desire to secure by Letters Patent of the United States, is:

ed adjacent to one another and separated by an insulating medium.

4. In combination, an evacuated envelope containing inert gas and a plurality of photoelectric units separated by a partition of insulating material to form compartments, the dimension and configuration of said partition being such that heat and gas are readily transferred between compartments but light and electrons are precluded from passage.

5. In combination, an evacuated envelope containing inert gas and a plurality of photoelectric units separated by a partition of insulating material to form compartments, the dimension and configuration of said partition being such that heat and gas are readily transferred between compartments but light and electrons are precluded from passage, the respective cathodes of said units being constituted of light sensitive surfaces formed on opposite sides of the insulating material.

- In witness whereof, I have hereunto set my hand this 23rd day of April, 1929.

WILLIAM E. STORY, JR.

1. In combination, an evacuated envelope containing a plurality of photo-electric units, each comprising a 1i ht sensitive cathode and a cooperating ano e, said cathodes being mounted on a common insulating material.

2. In combination, an evacuated envelope :ontaining a plurality of photo-electric umts each comprising a light sensitive cathode and a cooperating anode, said units being mounted adjacent to one another and electrically independent of one another.

3. In combination, an evacuated envelope containing a plurality of photo-electric units, each comprising a light sensitive cathode and a cooperating anode, said units being mount- 

